Sporulation by Races 0, 2, and 3 of Cochliobolus carbonum on Synthetic Medium and Sterilized Corn Leaves. H. G. Welz, formerly Postdoctoral Research Associate, Tropeninstitut der Justus-Liebig-Universität, 35390 Giessen, Germany. S. Leath, and K. J. Leonard. USDA, ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 77:1153-1157. Accepted for publication 18 August 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-1153.

Isolates of races 0, 2, and 3 of Cochliobolus carbonum collected from two locations in North Carolina were grown in vitro at 20, 24, or 28 C on potato-lactose agar (PLA) or on water agar with either autoclaved green corn leaves or senesced corn leaves. Races, temperatures, and media all significantly affected sporulation. Temperature × race and substrate × race interactions were not statistically significant. Therefore, it seems unlikely that differences in sporulation by races 2 and 3 on corn are influenced differentially by temperature or simple nutritional factors. Averaged over all factor levels, race 2 sporulated best, followed by race 3 and then race 0. The races ranked in the same order when compared for parasitic fitness in an earlier survey of race frequency changes over time in the two fields where these isolates were collected. In another experiment with 318 C. carbonum isolates from these two fields plus 14 from a field in Tennessee, race 2 mycelium grew significantly faster on PLA than mycelium of race 3 or race 0; any difference between race 3 and race 0 was not significant. Thus, mycelial growth rate may be a less reliable indicator of fitness than sporulation in vitro.

Keyword(s): Bipolaris zeicola, Helminthosporium carbonum, maize, Zea mays.